Optical switches have been used in a variety of environments to detect fluid levels. The switch components are generally located in a housing, where the housing is fixed with respect to the fluid level. A fixed housing avoids bending of optical fibers, as bending can cause attenuation and fracture of the optic fibers. One optical switch embodiment with a flexible cable is shown in U.S. patent application Ser. No. 12/577,572, and U.S. application Ser. No. 12/576,894, (both hereby incorporated by reference) and in PCT/US2007/70122, filed on May 31, 2007, hereby incorporated by reference.
Several embodiments of these switches use an optical switch cable that is tethered to the tank, where the switch floats in the fluid. A moveable member is positioned in the switch body, where the moveable member moves to a position within the switch to modify the transmission path of light between an emitting fiber, and a receiving fiber. The light path between fibers can be direct, where the fibers are directly optically aligned or aligned by a bounced specular reflection path where polished or mirrored surfaces are used to modify the path of the emitted beam as desired, or indirect, in the sense that a glowable material is used and illuminated by the emitting light fiber, where the glowable member remits the light or reflects the light into a multitude of directions (e.g. scatters the light, such as by diffuse reflection), and hence the material appears to “glow” or be illuminated from an area much larger than the spot where the optical fiber's emitted light beam is incident on the material. One configuration of an optical switch is shown in FIG. 5, and shows a housing containing two optical fibers, one connected to a light source, the other connected to a light detector, usually remotely located from the housing. The two fibers are separated by a gap, and a moveable member, such as a slug or ball, moves in the gap, such as in an ampoule. As the housing tilts due to rising or falling fluid levels, the moveable member can interrupt of modify the transmission of light across the gap from the emitting fiber to the receiving fiber. The change in the receiving light is then detected at the light receiver. Other versions of optical switches are referenced in the above mentioned applications.
There is a need for optical switches to detect fluid level in a wider class of applications, in particular, tank environments, including a floating roof environment.